RACH procedures for non-terrestrial networks for user equipment
Methods and systems to enhance NR RACH procedure to accommodate non-terrestrial networks (NTN) are disclosed. The length of the RAR window may be extended. A NTN-RNTI associated with the time-frequency resources used for the PRACH preamble may be used to scramble the CRC of DCI used for downlink assignment in the RAR. The DCI content may include information on the associated PRACH preamble to assist the UE in distinguishing between RARs generated as a response to PRACH preambles transmitted by different UEs from different system frames. The NTN-RNTI may contain information on the system frames when the UE sends the PRACH preamble. The RA-RNTI associated with the time-frequency resources used for the PRACH preambles transmitted from different frames may be used to scramble different subsets of the CRC of the DCI format 1_0 to assist the UE in distinguishing between RARs generated in response to the different PRACH preambles.
1. A method of accessing a communication network by a wireless user equipment (UE), the method comprising:
transmitting, by the UE to a base station of the communication network, a physical random access channel (PRACH) preamble during a frame of a frame structure that includes a plurality of frames to request access to the communication network;
receiving, by the UE, a random access response (RAR) message from the base station during a RAR window, wherein the RAR window spans two frames of the frame structure; and
determining, by the UE, whether the RAR message received from the base station is intended for the UE based on an indication in a downlink control information (DCI) that schedules the RAR message, wherein determining that the RAR message is intended for the UE comprises:
determining, by the UE, a radio network temporary identifier (RNTI) based on time-frequency resources of the frame used for transmitting the PRACH preamble;
detecting, by the UE, that a cyclic redundancy check (CRC) of the DCI of the RAR message is scrambled by the RNTI; and
determining, by the UE, that a field in the DCI identifies a frame number of a triggering PRACH associated with the RAR as an even frame or an odd frame, and wherein the frame number matches with the frame used by the UE for transmitting the PRACH preamble.
2. The method of claim 1 , further comprising:
determining, by the UE, a timing advance (TA) value, wherein the TA value is adaptable to align a frame structure between the UE and the base station to account for a propagation delay between the UE and the base station.
3. The method of claim 2 , wherein the TA value is determined based on location information of the UE.
4. The method of claim 2 , wherein the TA value assumes the UE is at a common reference position of a coverage area of the base station.
5. The method of claim 2 , wherein receiving the RAR message comprise:
offsetting a start of the RAR window from an end of the PRACH preamble transmitted from the UE by the TA value.
6. The method of claim 2 , wherein transmitting the PRACH preamble comprise:
transmitting the PRACH preamble using the TA value to account for the propagation delay between the UE and the base station.
7. The method of claim 1 , further comprising:
receiving, by the UE from the base station, a time gap value;
receiving, by the UE from the base station, a downlink transmission; and
transmitting, by the UE to the base station, an acknowledgement of the downlink transmission, wherein the time gap value indicates a delay between receiving the downlink transmission and transmitting the acknowledgement of the downlink transmission.
8. The method of claim 7 , wherein the time gap value is adaptable to align the acknowledgement of the downlink transmission with an uplink slot of the frame structure.
9. The method of claim 7 , wherein the time gap value indicates the delay between receiving the downlink transmission and transmitting the acknowledgement of the downlink transmission as a number of slots of the frame structure.
10. The method of claim 9 , wherein the delay comprises a maximum value of 31 slots.
11. The method of claim 1 , wherein transmitting by the UE the PRACH preamble comprises:
transmitting repeatedly the PRACH preamble using identical time-frequency resources of a plurality of frames of the frames structure, wherein the PRACH preamble is transmitted with increasing power over the plurality of frames.
12. Baseband circuitry, comprising:
a memory comprising one or more instructions; and
one or more processors configured to execute the one or more processors to cause the baseband circuitry to perform operations comprising:
transmitting to a base station of a non-terrestrial communication network a physical random access channel (PRACH) preamble during a frame of a frame structure that includes a plurality of frames to request access to the non-terrestrial communication network;
receiving a random access response (RAR) message from the base station during a RAR window, wherein the RAR window spans two frames of the frame structure; and
determining whether the RAR message received from the base station is intended for a user equipment (UE) based on an indication in a downlink control information (DCI) of the RAR message wherein determining that the RAR message is intended for the UE comprises:
determining, by the UE, a radio network temporary identifier (RNTI) based on time-frequency resources and a frame number of the frame used for transmitting the PRACH preamble, wherein the frame number is identified as an even frame or an odd frame; and
determining, by the UE, that a cyclic redundancy check (CRC) of the DCI of the RAR message is scrambled by the RNTI.
13. The baseband circuitry of claim 12 , wherein the operations further comprise:
determine a timing advance (TA) value, wherein the TA value is adaptable to align a frame structure between the UE and the base station to account for a propagation delay between the UE and the base station.
14. The baseband circuitry of claim 13 , wherein the TA value is determined based on location information of the UE.
15. A user equipment (UE) device comprising:
at least one antenna;
at least one radio, wherein the at least one radio is configured to communicate with a base station of a non-terrestrial communication network using the at least one antenna; and
at least one processor coupled to the at least one radio, wherein the at least one processor is configured to perform operations comprising:
transmitting to the base station a physical random access channel (PRACH) preamble during a frame of a frame structure that includes a plurality of frames to request access to the non-terrestrial communication network;
receiving a random access response (RAR) message from the base station during a RAR window, wherein the RAR window spans a plurality of frames of the frame structure; and
determining whether the RAR message received from the base station is intended for the UE based on an indication in a downlink control information (DCI) of the RAR message wherein determining that the RAR message is intended for the UE comprises:
determining, by the UE, a radio network temporary identifier (RNTI) based on time-frequency resources of the frame used for transmitting the PRACH preamble; and
detecting, by the UE, that a portion of a cyclic redundancy check (CRC) of the DCI of the RAR message is scrambled by the RNTI, wherein the portion of the CRC of the DCI scrambled is identified based on an odd frame or an even frame of the frame used by the UE for transmitting the PRACH preamble.
16. The UE of claim 15 , wherein the operations further comprise:
determining a timing advance (TA) value, wherein the TA value is adaptable to align a frame structure between the UE and the base station to account for a propagation delay between the UE and the base station.
17. The UE of claim 16 , wherein the TA value is determined based on location information of the UE.